1. Field of the Invention
The present invention relates to a fluorine-containing graft copolymer, which is effective as a resin component when contained in a dry-type toner or wet-type toner for developing latent electrostatic images for use in electro-photography, and to the dry- or wet-type toner which comprises the above-mentioned fluorine-containing graft copolymer.
2. Discussion of Background
In recent years the electrophotographic technology has been applied not only to an electrophotographic copying apparatus, but also to a laser beam printer. The necessity for high-speed recording therefore becomes important in this field, so that a heat-application roller is widely used as an image fixing means because of its high-speed image fixing performance.
Furthermore, demands for image fixing performance of recorded images are diversified. For example, copied or printed images formed on a sheet of paper by the electro-photographic technology are used as direct mail advertising, which is sometimes utilized by folding an image-bearing sheet of paper. In addition, printing or copying is performed on a thick sheet such as a post card. Under such circumstances, excellent image fixing performance of toner images is necessarily required.
In Japanese Laid-Open Patent Application 50-134652, there is proposed a toner for use in an electrophotographic apparatus comprising a copolymer resin of styrene - acrylic monomer having a degree of dispersion of 3.5 to 40, which serves as a binder resin. This toner can decrease a hot off-set phenomenon in the course of image fixing operation.
In Japanese Laid-Open Patent Application 62-115170, a resin composition of a toner for use in an electrophotographic apparatus is disclosed. This resin composition is prepared by mixing copolymer resin (A) of styrene - acrylic monomer having a weight-average molecular weight of 10,000 to 30,000 and a glass transition temperature ranging from 60.degree. C. to 70.degree. C. and copolymer resin (B) of styrene - acrylic monomer having a weight-average molecular weight of 200,000 to 400,000 and a glass transition temperature ranging from 55.degree. C. to 65.degree. C. at a mixing amount ratio of 90:10 to 50:50, and the thus prepared resin composition shows a melt viscosity of 10,000 poise or less at 140.degree. C.
In addition to the above, many proposals are made to obtain improved toners having high image fixing performance adaptable to a high-speed development mode and sufficient resistance to blocking and hot off-set phenomenon.
However, when the aforementioned conventional toners for use in an electrophotographic apparatus are used in a wet-type developer, their dispersibility is not stable in a carrier liquid such as aliphatic hydrocarbon. When used as a dry-type developer, conventional toners cannot be satisfactorily fixed on a transfer sheet if their energy for image fixing is small.
Accordingly, there are no toners which can satisfactorily show the image fixing performance without the hot off-set phenomenon in a high-speed development mode, and which have resistance to blocking and sufficient dispersibility in a carrier liquid.
With the above-mentioned problems taken into consideration, a resin component of the toner becomes the object of attention. There are conventionally known as the resin component a fluorine-containing acrylate type copolymer, a fluorine-containing polyether type copolymer, fluorine-containing urethane type oligomer and the like.
Although the above-mentioned polymers show good water and oil repellency when used in a toner, they have shortcomings in the durability, flexibility, adhesiveness which relates to the durability, and dispersibility.
As the flexibility of the conventional fluorine-containing polymers is increased, the initial performance is degraded and durability is decreased; and the fluorine-containing polymers having sufficient durability lack in flexibility.
It is difficult for conventional fluorine-containing polymers serving as a resin component in the toner to satisfy all the properties such as water- and oil-repellency, durability, flexibility, adhesiveness and dispersibility at the same time.